Here’s a riddle: Picture a group of rich people in New Jersey’s top 1 percent, spending millions of dollars to elect a candidate who supports Donald Trump and Chris Christie.

Are you thinking about the leadership of the state’s largest teachers’ union, the New Jersey Education Association?

Neither did I. But that’s the winning answer.

In what is shaping up to be the most expensive legislative race in the state’s history, the NJEA is throwing all it has into the effort to elect Fran Grenier to Senate, and to defeat Senate President Steve Sweeney (D-Gloucester).

It’s an infuriating move to many Democrats, since they will now have to spend huge sums in defense of Sweeney, money they hoped to use to expand their majority in the Senate.

The NJEA is furious at Sweeney because he pushed the 2011 bill limiting pension and health benefits for public workers, and because he broke a big promise to the union. He vowed to put a Constitutional amendment on the ballot that would require the state to make full pension payments each quarter, but reversed course when he became convinced voters would reject it in the wake of the summer’s big increase in the gas tax.

We’ll never know, but most people I talked to in both parties agree with Sweeney’s political prediction, that the effort would have backfired.

Never mind, though. To the union, this defiance must be punished, even if it means weakening Democratic allies and boosting a Trump supporter.

They have flooded the airwaves in Sweeney’s district, and stuffed mailboxes with pamphlets that are crammed with lies, like saying he works as a lobbyist and collects multiple public pensions, with photo-shop pictures showing Sweeney stuffing $100 bills into his suit pocket.

Sweeney is part of the South Jersey machine run by George Norcross, who commands the loyalty of the largest faction in the Democratic legislature. In an unusual twist, though, the mailers are going to legislative offices as well, including those far from Sweeney’s district.

Get the message, legislators? You mess with this union, and you die.

My own hope is that Democrats wake up and see the NJEA for what it is: The most regressive special interest group in the state, run by a cabal of fat-cats who are enriching themselves by squeezing their middle-class membership.

Classroom teachers in New Jersey earn an average of about $70,000 a year before taxes, according to state data, and they pay $866 a year in dues, according to the union. They are solidly middle-class.

Union leaders, though, are not. Eight members of the leadership team have earned more than $2 million over the last six years in salary and benefits, with top honors going to Vincent Giordano, a long-time executive director and vice-president, who averaged about $700,000 a year over that period.

“They work tirelessly and dedicate their lives to this work,” says the union spokesman, Steve Baker.

Okay, but so do most regular teachers. Why should Giordano earn 10 times as much?

Those fat salaries, and the endorsement of a Trump supporter, has some teachers in the district grumbling.

“I’m not happy that my dues are going to support someone who backs Trump, and I’m not alone in that,” says Donna Ragonese, an 8th grade literacy teacher in Franklin Township. “And we all want to make a decent living, but those salaries are so far above what teachers make, it’s a little disappointing.”

Classroom teachers, please take note. To criticize the NJEA is not to criticize teachers. Most of us can remember a devoted teacher who changed our lives. I have a handful. And the state’s second teachers’ union, the American Federation of Teachers, led by Randy Weingarten, gave Sweeney itsfull-throated endorsement as a champion of public education.

It’s past time to take a more critical look at the NJEA, and to see how it undermines progressive causes in New Jersey. Backing this Trump supporters is only the most obvious case.

The NJEA is no friend of poor children in New Jersey. It protects bad teachers by insisting on blanket seniority protections. It works to limit the expansion of the most successful charter schools, even in poor cities, where African-American and Latino families flock to them.

And it fights, even during this fiscal crisis, against modest cuts to generous health care plansthat would qualify as “platinum” level under Obamacare. That leaves less money for progressive causes, like expanding affordable housing, preschool programs, or drug treatment programs.

Grenier is not the sort you’d expect to win union support. He is an arch-conservative who says he supports Trump’s agenda, and was so enthusiastic about Christie’s presidential campaign that he dropped everything to work for the governor in New Hampshire. He denies climate science.

His knowledge of state issues, including education, is flimsy. He told the Philadelphia Inquirer that each town should get the same level of state aid per student, regardless of its wealth, the core of an awful plan put forward by Christie last year. That would force massive teacher layoffs in urban districts like Newark, which would have to cut its budget by more than half. He now claims he was misquoted, but won’t say if he asked for a correction at the time.

He says the state must cut spending, but he can’t name a single program he would target other than cancelling the Statehouse renovation. “I’m looking forward to digging in and finding out that stuff,” he says.

You get the idea. To the NJEA, Grenier is a battering ram to get at Sweeney. The less people talk about him, the better.

But what if he winds up in the Senate? This is shameless stuff. And it’s beyond disappointing that Phil Murphy, the Democratic candidate for governor, is doing nothing to stop it. He has the enthusiastic endorsement of the NJEA, but the union says he hasn’t even asked them to cease-fire.

Murphy’s campaign won’t comment, but the rest of the Legislature is watching. Some worry that this will create a rift between Murphy and Democrats allied with Sweeney and Norcross, one that could kneecap Murphy’s agenda. Others are hoping for just such a rift, saying Norcross and his crew need to be brought down a peg after steering the party towards the center during the Christie years.

My guess is the NJEA is making an enormous mistake, that Sweeney will win, and that Murphy will emerge weakened as legislators see that he refused to throw a fellow Democrat a life-preserver in his hour of need.